Boride coatings are difficult to form on substrate surfaces composed of carbon or graphite. The most common method for applying a boride coating to a carbon or graphite substrate is by means of chemical vapor deposition (CVD) whereby the substrate is heated in the presence of a gaseous mixture such as BCl.sub.3 +TiCl.sub.4 +H.sub.2. This process is expensive and is a line of sight process which makes coating uniformity a problem particularly for an object such as a multifilament yarn. Other methods for forming a boride coating such as plasma spraying have been less successful in that cracks form on cooling.